Conventionally, there is a known multilayer wiring board obtained by making interlayer electrical connection between wirings arranged via insulating resin layers. For such an interlayer connection method, there is a known via-hole conductor as formed by filling a hole provided in an insulating resin layer with conductive paste. In another known via-hole conductor, metallic particles containing Cu are applied instead of the conductive paste, and fixed together by an intermetallic compound.
Concretely, for example, Patent Document 1 below discloses a via-hole conductor having a matrix-domain structure in which a plurality of domains made of Cu particles are dotted in a CuSn compound matrix.
Also, for example, Patent Document 2 below discloses a sinterable composition for use in via-hole conductor formation, which includes a high-melting-point particle-phase material that includes Cu, and a low-melting-point material that is a selected metal such as tin or a tin alloy. Such a sinterable composition is a composition sinterable in the presence of a liquid phase or a transient liquid phase.
Also, for example, Patent Document 3 below discloses a via-hole conductor material in which alloy layers with a solidus temperature of 250° C. or higher are formed on circumferences of copper particles by heating conductive paste, which contains Sn—Bi metallic particles and the copper particles, to a temperature greater than or equal to the melting point of the Sn—Bi metallic particles. Such a via-hole conductor material is described as achieving high connection reliability since interlayer connection is made by joining alloy layers with a solidus temperature of 250° C. or higher and the alloy layers do not melt in temperature-cycling and reflow resistance tests.
Also, for example, Patent Document 4 below discloses a multilayer wiring board provided with via-hole conductors which contain copper and tin in a total amount of 80 to 97% by weight, along with bismuth in a proportion of 3 to 20% by weight.